Re: [boost] lexical_cast optimization

Subject: Re: [boost] lexical_cast optimization
From: remi.chateauneu_at_[hidden]
Date: 2008-12-05 22:35:19

This is about 10%  faster on a Pentium:

    {
      for(const char* p = str_value; size; ++p, --size)
      {

Jonathan Brannan wrote:
> we have found that atoi/strtol/strtoll/strtod are slow compared to the
> optimized output (gcc -O2/3) of a very simple * 10 loop.  The C number
> converters work for a large varity of bases, which makes them slower
> than needed for base 10.
>
> we use something like:
>
>   template<typename TInteger>
>     bool validated_to_unsigned_int(
>         const char* str_value, size_t size,
>         TInteger& result)
>     {
>       size_t i = 0;
>       for(const char* p = str_value; i < size; ++p, ++i)
>       {
>         char digit = *p;
>         if (digit >= '0' && digit <='9')
>         {
>           result = result * 10 + digit - '0';
>         }
>         else
>         {
>           return false;
>         }
>       }
>       return true;
>     }
>
> with wrappers for signed and ones that throw exceptions.  We have a
> few converters that are faster, but only without error checking (base
> 16 conversion with lookup table works for small numbers, for example)
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